Stone asphalt road and method of preparing and laying the same



Oct. 13, 1931. D. M K. HEPBURN 1,827,522

STONE ASPHALT ROAD AND METHOD OF PREPARING AND LAYING THE SAME v Original Filed Nov. 3. 1925 M m G The principal objectofthe "is'to provide a slowsetting bituminous 'stock material for road making. or surfacing which Patented Oct. 13,1931

UNITEDISTATES PATENT OFFICE DONALD MCKNIGHT HEPBURN, OE -PHILADELPHIA, PENNSYLVANIA, ASSIGNOR 'IO AMIESITE ASPHALT COMPANY OF AMERICA, OF PHILADELPHIA, PENNSYLVANIA,

A CORPORATION OF NEW JERSEY STONE ASPHALT ROAD AND METHOD OF PREPARING AND LAYING THE SAME Original application filed. November 3, 1925, Serial No. 66,586. Divided and this application flied March 29,

. 1926. Serial No. 98,383.

My invention relates to bituminous road surfacing materials or compounds and to the manufacture thereof, andv to roads formed therefrom, the said materials being of such character that they can be mixed at the quarry where the stone originates or where the aggregate originates, and can be shipped in railroad cars, or trucks over the highways, and can be'laid at the temperature of the air Without any further preparation, or maybe held in storage/to be employed at any future time without further preparation. In accordance with the invention the stone or other aggregate is dried and cleaned and prepared for the storing or absorption of a solvent therein before the aggregate comes into contact with the bitumen'which is to be used as a binder. This drying and cleaning is done without substantially heating the stone or aggregate and thereafter the solvent is added. After the solvent has been absorbed by the stone, the latter is mixed with the bitumen. The solvent contained in the stoneis then slowly absorbed by the cold bitumen which is by this means maintained in a plastic condi tion. The thorough drying of the stone by my process gives me ample capaclty of storing the amount of solvent required tohandle the'material at the temperature of the air,

and the reabsorption of the solvent from the stone into the bitumen extends over a period of many daysor even weeks. The material manufactured by this method can thus be shipped long distances and successfully unloaded and laid in place at the temperature of the air. I have inactual practice shipped thematerial hundreds of miles, taking ten days or. more in transit, and have experienced notrouble inunloadingor laying. Themaskid surfaces. i y

inventlon, then,

material is adapted to be transported and laid at atmospheric temperatures and without any preliminary heating. I I

parent from the following specification and claims.

The drawing is a diagrammatic View of an apparatus by means of which the manufacture of my improved road composition is facilitated.

Referring to the drawing, 1 represents a revolving drum which is adapted to serve as a cleaner and dryer for the crushed rock or other aggregate which is to be used. As illustrated this drum is inclined to enable the material to progress through it. Suitable means, such as a motor 2, is provided for rotating the drum.

An elevating conveyer 3 is provided for delivering the crushed rock or aggregate to the receiving end of the drum. Before being de llveredto the conveyer the rock or other aggregate is suitably graded as to size by screens or other devices which are not shown.

I From the drum 1 the aggregate is discharged through a chute 4 into a weighing hopper 5. From the weighing hopper the aggregate is discharged into a suitable mixer 6 which may be provided with a steam-jacket -7. From the mixer the material can be disthe drum 1 by means of a suitable fan 9.

For heating the air delivered by the fan, or at least some of the air, I provide a suitable heater which is shown as being an oil burner 10 Preferably I heat only a portion of the air supplied to the fan and I, therefore, provide a funnel 11 through which the heated air is delivered, other air being drawn into the fan around the funnel.

In practicing my improved method, the stone is delivered by the conveyer 3 into the ,drum- 1. ,By reason of the rotation of the drum, the aggregate is caused to slowly progress downward through the drum, and on doing so it is acted upon by the air delivered by the fan 9. In practice I have found that a large fan is desirable, and for a drum four feet in diameter I prefer a fan having a capacity of approximately 140,000 cubic feet of air per minute. This large volume of air flowing through the drum in opposition to the movement of the aggregate removes all dust and small particles from the aggregate thus thoroughly cleaning it. 7 The. airis used as a "dryingmediumfor the aggregate as well as a cleaning medium therefor, and to facilitate the drying action 'the air is orrnaybe slightly heated. The heating means for the air has already been described, and it will be understood that the fan serves to draw in a large volume of air directly from 1 the atmosphere, andalso serves to idraw'in acaused to evaporate to anyjappreciable exgate which, as already stated, is at only T3. Lfew degrees above the"atmospheric'ltemperaatmosphere. I prefer to so control the :tem'- peratureof the air delivered to'the drum that the aggregate will not be raised more than sixlor'seven degrees above the atmospheric temperature vIhav'e found that in dry clear summer weather I can eliminate theburner for artificially heating the air,'thef required drying of the stone being effected by theatmospheric airwithout heating. I I

, By means of the weighinghopper definite batches .of' the aggregate of predetermined weight ,canfbe delivered to the mixer 6, and from the foregoing description it will 'be seen that the aggregate thusdelivered hasbeen thoroughly cleaned and" thoroughly dried without, however, having the temperature thereof raised much above the atmospheric temperature. Thisavoidance of any substantial increase in thetemperature of the aggregate is important" for a -reason'whic'h will presently appear. V i I p As soonas a batch of the aggregate is delivered into-the mixer, which'is in operation, i "I add to the aggregatea suitablefmateri al which is adaptedto serve as a solvent for: the

asphalt or other bitumen which is'to be subsequently added. 7 This solvent should beta slowly volatile one such askerosene or other .oil having a flashtest, or evaporating temperature, ranging from 120 degreesFJto-1 5O degrees F. It will befseen that I seleetra ,solventwhich will not rapidly evaporate at atmospheric temperature, and which, therefore, willnot' within a; reasonable i'time'be tent by reason ofthe contact with the'aggreture. ,The amount of solvent which'is added is carefully, predetermined by test so that there will be no excess beyond what' can'be retained and absorbed 'by' the thoroughly ,dried "and slightly porous surfaces of the v stone. I have found that when the stone is thoroughly dried, as described, a considerable amount of solvent can be absorbed there-- by, and the operation of the mixer is continue'd'until all of'the'surfaces of the aggregate arethoroughly saturated with the sol-- vent and until the solvent is completely abisorbed.

After the solvent hasbeen absorbed, I then preferably add asubstance which serves to toughen or thicken the bitumen. This substanceis'preferablyhydrated lime andI add from one-half I to one percent by actual *wei'ght. The mixing is continued untilta thoroughly homogeneous mass is produced,

with the lime uniformly distributed as a surface coating over thepieces, of "stone' or aggregate. I have found by actual practice that either caustic. lime or hydrated lime will produce the sameresults but,rinasmuch as the caustic lime is harder-to handle, Iprefer to use. thehydrated lime. Y Y

I then ;add the required quantity of the bituminous binder which hasbeen previously heated to atemperature of a'pproxinlately250 degrees F. or mores Preferably I use from 7 to "8% by weight of 'bitumen for the base course'material; 9 to 10%. for the wearing coursematerial; and 31/ 110 4% for the 'sealingcourse material. The mixing of. the

bitumenwith the aggregate is continued until all pieces ofthe, aggregate'have been thoroughly coated. It will be understood that the heating of thebitumen is primarily for the purpose of more easilysecuring the requirednniformity of mixture 'and the required uniformity of the distribution ofthe b1tumen over the surfaces of thepieces of stone :oraggregate. This heating T is not for the'purpose "of facilitating the subsequent layingiofthematerial, as the inaterialis 211- lowed tobecome cold before being'laid. I

The steamgjacketmay be used for theEpurpose of'maintainingtheheat of the bitumen duringthe Iinalniixing operation, but'is not 3 used during the preliminary. mixing opera- ,tions when" the solvent and the lime are added. After themixing'with thebitumen' has "been completed "the mixture is then discharged from the mixer intojthe (,8 -orzother transporting means. g i V The'hydrated limewhich Iadd to-the'mix ftu-re or my "material is used :to' toughen the binder, particularly at the points. of contact with-the stone. This also increases the thick- I, messof the bitumen on1the individualstones of :the" aggregate; a resultthat is very beneficial and desirable. The lime,:being added .before thebitumen is added-to the mix, is :very uniformly distributed throughout the entiremass. I ,7

. According to prior practice, there arethree methods-of-establishing a bond between the aggregate and the bitumen: first, the 'emi l .sionmethodin which the'bitumen is emulsi- 'fied with water; s'econ'd,the heating of both railway car the aggregate and the bitumen to about 27 5 degrees F.; and third, the cold methods of combining the aggregate and bitumen by thining the latter with a solvent. In the emulsifying method, the aggregate absorbs a large quantity of the water or, in other words, becomes saturated. As the result of this method a comparatively thin coat of bitumen is left on the aggregate, and the mixture has a very temporary life, with a relatively poor bond between the bitumen and the aggregate. By the hot mix method the heat, which is applied to both the aggregate and the bitumen, is used as a distributing agent to keep the material plastic; and the result is that the material must be placed and compacted in the pavement at a high temperature. By the method wherein the solvent is added to the asphalt as a distributing agent, suflicient solvent must be added to handle the asphalt cold. This results in too thin a coat on each individual stone in the aggregate.

From the foregoing it will be apparent that my improved composition differs radically from prior practice in that I neither apply heat to the entire mass to effect distribution nor add a liq uefier to effect distribution. I apply heat only to the bitumen, and mix this heated bitumen with cold aggregate in order to obtain a thick coat of bitumen which is chilled in coming into contact with the aggregate. This gives me a thicker coating of asphalt on the individual pieces of aggreate than could be obtained with hot stone. I store the solvent in the stone so that it is not used at all as a fiuxing material or liquefier to aid in coating the stone. The solvent having been stored or absorbed in the aggregate before coating and the asphalt having been chilled when coated on the stone, I have a physical condition of the bitumen that holds the heavy coating on the stone. This bitumen, now being cold and far below the melting point thereof, is slowly attacked by the solvent and, due to the fact that the bitumen and stone are cold, the action of the solvent is retarded and this facilitates the unloading and laying of the material days after the material has been mixed. I find in actual practice that the slow absorbing of the solvent by the bitumen tends to draw the bitumen further into the surface of the stone. Any solvent that is absorbed by the bitumen must be replaced by the bitumen penetrating the pores of the stone occupied by the solvent. This not only retards the action of the solvent but also increases the bond between the stone and the bitumen.

In case additional heat is needed in the final mixing to produce a uniform coating of the gregate. In this way I get a thorough coating without the use of a liquefier in the bitumen or heat in the aggregate.

As the material in forming a road is all laid at the temperature of the air, uniform compression is obtained throughout the entire mass. As admitted by experienced pavement engineers, no road rolling in a short space of time by a mechanical roller having a wide contact with the pavement can roll a pavement material to ultimate compression. With my method of manufacture, advantage is taken of the traffic over the road to compact the road and bring it to ultimate compression, as the material is in its original cold and plastic condition so that it can benefit by the compression of traffic.

I claim:

1. The method of mixing a bituminous paving composition, which consists in taking a stone aggregate, subjecting said aggregate to a current of air carefully regulated as to temperature so as to thoroughly dry the aggregate without materially increasing its temperature, thereafter applying to the stone a bitumen solvent, and subsequently adding bitumen to the aggregate.

2. The method of mixing a bituminous paving composition, which consists in taking graded pieces of stone constituting an aggregate, passing thereover a large volume of air to dry them and remove all dust and fines without materially elevating the temperature of the stone, applying to the said pieces of stone a volatile bitumen solvent, and subsequently adding bitumen to the aggregate.

3. The method of mixing a bituminous paving composition, which consists in subjecting graded pieces of stone constituting an aggregate to a current of heated air to dry them and remove all dust and fines, the heat being controlled to avoid heating the stones substantially above atmospheric temperature and the air being in large volume to facilitate the drying operation, applying to the said pieces of stone a bitumen solvent, and immediately adding heated melted bitumen to the aggregate which is maintained at substantially atmospheric temperature until engaged by the bitumen.

DONALD MCKNIGHT HEPBURN. 

